1. Field of Invention
The present invention relates to an organic-inorganic hybrid hollow fiber membrane technique, and more particularly to a method for preparing an aromatic polyamide porous hollow fiber membrane. The aromatic polyamide is poly-p-phenylene terephthalamide (PPTA).
2. Description of Related Arts
In general, a phase-to-phase interface layer exists between different polymers. Due to existence of the phase-to-phase interface, the polymers are easy to have separation phenomena during the process of manufacture or utilizing. Thus, the phase separation phenomena can be utilized during the process of membrane manufacture, so as to optimize the performance of the membrane.
When the organic polymers are hybridized and mixed with the inorganic particles, the inorganic particles are usually high surface energy substance, but the organic polymers are usually low surface energy substance. Thus, the mixture of the organic polymers and the inorganic particles will inevitably form new phase interfaces, so as to form micropores taking advantage of phase separation. The conventional porous membranes have advantages of good flexibility, high permeability and simple preparation process, but the solvent resistance, corrosion resistance and temperature resistance thereof are poor. At the same time, in spite of the high strength, high corrosion resistance and high temperature resistance, the inorganic membrane is fragile and difficult to manufacture and has high cost. Thus, the organic-inorganic hybrid membrane has both the characteristics of organic components and inorganic components and thus has good separation properties and physical and chemical stability.
Poly-p-phenylene terephthalamide (PPTA) is a typical para-aromatic polyamide which is a rigid macromolecule and an important raw material for manufacturing Kevlar® fiber. Having excellent high temperature resistance and solvent resistance, the PPTA is a satisfying material for manufacturing high-performance porous hollow fiber membrane. However, since the melting point (over 500° C.) of the PPTA is below the decomposition temperature, the PPTA can not be fabricated by melt spinning technique. In addition, since the PPTA rigid macromolecule has a smaller entropy of free energy change than the flexible macromolecule during the dissolution process and thus is difficult to be dissolved in the conventional solvent and only capable of being dissolved in strong acid such as sulfuric acid and chlorosulfonic acid. P. Zschocke et al. produce a PPTA flat membrane and test the flux of the PPTA flat membrane in different types of solvents. Pure water flux of the PPTA flat membrane is only 12.8 L/(m2 d) (3 MPa). [Shown as Solvent resistant membranes from poly-(p-phenylene-terephthalamide), Desalination, 34 (1980):69-751 Katsumori Nakura et al. test the PEG (50000) rejection performance of PPAT flat membrane in different kinds of solvents. Though the rejection rate is high, there is also the problem of low flux.
During the preparation process of the PPTA spinning solution, stir and deaeration of high viscosity casting solution are two difficult problems to be solved. The dissolved method of PPTA in concentrated sulfuric acid is known to all. However, dissolving high viscosity casting solution in the conventional stirring vessel requires 2-3 hours, and the deaeration time thereof is even longer, which leads to the degradation of PPTA macromolecule, so that the mechanical properties of the hollow fiber membrane are influenced, and that the composite pore-forming agents are modified to cause blackening and deterioration of the casting solution.